The present invention relates to a device for controlling knitting machines of the type having stationary needle boards and a set of knitting carriages circulating in one direction above the needle boards and each including needle selection elements and a control unit for operating the needle selection elements, and a stationary central control unit including a main computer.
From the U.S. Pat. No. 4,510,774 a control device for straight and circular knitters is known which includes a stationary control part and a moving control part circulating with one of the knitting carriages and including a microprocessor with corresponding data processing peripherals. Both the stationary control part and the movable control part operate independently one of the other whereby the stationary part stores data for stationary structural units of the knitting machine and the movable part stores data for knitting patterns for one or more knitted products. Entry of data for the movable control part takes place during the stoppage of the machine by means of a special reader or via a cable leading to the stationary control part. Flexible cables are used for transmitting commands for the pattern dependent needle selection and for the actuation of the movable knitting carriages, the flexible cables being connected to the movable control part on the carriage.
This prior art solution has the disadvantage that data transfer from and to the movable control part can occur only during the standstill of the machine. During the working cycle of the machine no correction or change of the knitted pattern is possible. Moreover, an additional carriage which is not used for the actual knitting process is necessary for supporting the movable control part.
Known is also a control arrangement for straight and circular knitting machines having circulating set of knitting carriages, a central control unit arranged at the center of circulation of the knitting carriages and rotating in synchronism with the latter, the central control unit including a main computer connected via trailing cables to auxiliary control units on respective knitting carriages. Each knitting carriage supports setting members for selection of needles and controlling the switching functions and also includes sensors for controlling the timing of the needles. All information for controlling the knitting process is stored in the main computer of the central control unit, the computer including an input and output, memory and the corresponding data and addressing buses.
The input of knitting information into the main microcomputer even in this case is possible only during the standstill of the machine by applying a data input apparatus, and so is also the central adjustment of the control elements to be activated such as for example for staggering or removal of the product. Also the overall actuation of the control field and a differentiated error indication in this prior art arrangement needs an improvement. The trailing cables have the disadvantage of a costly installation and design to meet the requirements for data transmission. Moreover, due to the continuous change in length during the circulation of the assigned knitting carriages on an elliptical track, the cables are subject to high loads and wear.
From the German publication DE-AS No. 2,658,588 a control arrangement for straight and circular knitting machines is known in which the pattern controlling pulses are transmitted to unidirectionally circulating knitting carriages from a stationary transmitter. Each knitting carriage is equipped with a convertor for converting the pattern signals into corresponding data words, a data processing unit including a microprocessor, a clock for delivering clock pulses to the data processing unit in synchronism with the needles, a memory for storing data pertaining to at least one knitted row, an end amplifier and a control device for operating the needles. For transmitting control information, there are devised acoustic and electromagnetic transfer elements, for example in the form of a light conductive rod, a bundle of light conductive fibers, a carrier frequency transmitter and the like. This known solution however permits the data transmission in one direction only and consequently there is no safeguard against a malfunction or errors. For transmitting error signals from the circulating knitting carriages to the stationary control unit it is necessary to use additional means which are not specified in this publication. In addition, susceptibility of the optical and electromagnetic data transmission means to interferences and soiling the reliability of the controlling operation is impaired.